1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus in which an analog-digital converted image signal is compressed and transmitted through a transmission medium or recording medium and, after that, the data is expanded and is digital-analog converted, and the image signal is generated.
2. Related Background Art
There is considered an image processing apparatus in which an image signal is divided into blocks each comprising a plurality of blocks and the data is orthogonal converted and the orthogonal converted data is quantized and variable length encoded so as to obtain a code amount in a certain range in said plurality of blocks.
As a method of selecting the plurality of blocks in such an image processing apparatus, a method as shown in FIGS. 1A and 1B is considered. FIG. 1A shows a whole image which is divided into (i=1 to n) blocks in the lateral direction and (j=1 to m) blocks in the vertical direction. Further, FIG. 1B shows one of the blocks divided in FIG. 1A and each block is further divided into (k=1 to l) blocks.
In the conventional image processing apparatus, the image signal is divided into blocks which is subjected to the orthogonal conversion as mentioned above. FIG. 2 shows a method of selecting (x) blocks in the case where the number of blocks is equal to x (x is an integer times as large as n) and they are x-block fixed length encoded.
In this instance, the value of (i) in FIG. 1A is sequentially increased from 1 to (n) and the value of (j) is properly changed within an x-block fixed length encoding. The value of (k) can be set to either the same value or different value.
For example, FIG. 3A shows a method of selecting every block when x=2n. FIG. 3B shows a method when x=4n. In FIGS. 3A and 3B, (t) indicates a time and the next block when t=1 is selected assumes t=2.
The image processing apparatus is constructed so as to select the block of the x-block fixed length encoding as mentioned above.
In the above conventional image processing apparatus, however, the Xth block in the x blocks which is subjected to the x-block fixed length encoding has a correlation for the horizontal direction of the image.
In the case where an error occurs in the Xth block in the x blocks, the blocks after the Xth block cannot be decoded and there are characteristics such that an error amount increases as the block approaches the end of the x-block fixed length encoding.
From the above description, there is a drawback such that the number of errors which occur gradually increases for the horizontal direction of the image and it becomes visually unsightly.